ON THE BRACHYUROUS DECAPODS OF THE CAPE. 



65 



Fam. GRAPSIDiE, M. E. 



Sub-genus? Gnathochasmus, M'L, 

 Cephalothorax sub-quadrate, with the back convex, and entire sides which are arched towards 



the eyes; the clypeus between the eyes is plane, entire, truncated and deflexed. 

 Exterior AntenncB produced as far as the middle between the eyes, and having the first joint 



transverse. 



External Pedipaljn very distant from each other; with the second joint very oblique at the 

 base, at the point sinuated, and of the same length as the third joint, which is concave in 

 the middle, and has a bearded crest continuous along its inner edge as far as the outer 

 part of the base of the second joint. 



Feet; first pair with thick and equal chelse. 



Abdomen in both sexes has seven segments. 



10. Dehaan has noticed the affinity between the two groupes, which he names Chasmagnathus 

 and Pachysoma. By them he passes from the family Ocypodidce to the family Grapsidcs. 

 The sub-genus or sub-section which I have just characterized under the name of GnatJwchasmus 

 comes exactly between Chasmagnathus and Pachysoma. It agrees with both in the remark- 

 able elevated crest, which stretches down obliquely from the inner angle of the third joint of 

 the external pedipalp to the outer angle of the base of its second joint. It has the thorax with 

 arched sides, like those of Chasmagnathus ; but then these sides are entire, like those of 

 Pachysoma. I may here observe, that Dehaan's name Pachysoma ought to be changed, as it 

 was assigned, long ago, by Mr. Kirby, to a division of the genus Scarabceus. See Horse 

 Entomologicse, part 2, p. 607. 



Sp. 21. ( ) Gnatliochasmus barbatus, n. s. 



Descr. Gnatliochasmus testa loevi, utrinque ad oculos deflexa regionibus sub-distinctis, lateribus 

 clypeoque marginatis integris ; manibus Isevibus glaberrimis crassis chelis sub-concoloribiis 

 latis convexis, pedibus Isevibus sub-compressis nigro-pimctatis tarsis sulcatis. 



Note. This crab is about an inch and a quarter long. 



Sub-genus. Sesarma, Say. 



Sp. 22. ( ) Sesarma reticulata, Say. 



Grapsus cinereus, Bosc. Hist. Nat. des Crust, vol. i. p. 204. tab. 6. fig. 1. 

 Sesarma reticulata, Say, Trans. Acad. Phil. vol. i. p. 73. tab. 4. fig, 5. 



Note. It is singular that I can find no good character whereby to separate this Cape crab from 

 the American species described by Bosc and Say. The latter, however, I only know from descrip- 

 tion. It is six lines long, whereas the Cape crab is more than an inch. Both are distinguished 

 from the Sesarma quadrata by their epistome being covered with granulations, so as to appear 

 finely reticulated. I dare say if we could compare the two crabs together we should be able 

 to discover a specific difference. The Cape crab has not the slightest vestige of granulation on 

 the shell of the cephalothorax. I have found in Cuba the species of Sesarma to live generally 

 under stones on the banks of the muddy mouths of rivers. Say's name, Sesarma, is adopted 



K 



